In regards to ABORTION: How STUPID do You have to be, to Believe the
PRODUCT of NORMAL Sexual Intercourse, IS NOT HUMAN LIFE, until it is
BORN?Why do We ABORT HUMAN LIFE? Because of the Fear of Over
Population on Planet earth, there are some Factions who Believe in Abortion;
Euthanasia; Sterilization; and the SELECT Harvesting of Non-Productive Human
Beings. The Debate, "When does Human Life Begin" Creates Emotional Reactions, and is
Responsible for both, HATE and MURDER. Contrary to what the EXPERTS Say, (Including
Socrates, Plato, and Aristotle), HUMAN LIFE whether started by, either CREATION or
EVOLUTION, Must be Continuous, or the Species will become Extinct! Human Procreation, is
Based on the followingFACT! Both the Male Sperm, and the Female Ovum, must be Viable in
order to produce Human Life. If either the male, or female are Void, they cannot Produce a
Human Product! Therefore; At Conception, the Micro Human becomes Entire, and its LIFE'S
EVOLUTIONARY PROCESS becomes Dependent, ONLY on the Nourishment of its Mother.The Words Embryo, and Fetus are only Definitions of the Evolutionary Progress, which adds
nothing to the Product! The Nice thing about Abortion and its Spin-offs is; It Creates New,
Potentially

Rich Professions, and JOBS for Many People.

The following is from

Encyclopedia Britannica's

Ninth Edition, 1878., Volume VIII. Page 163

A short Course in basic

EMBRYOLOGY

Embryology is a branch of biological inquiry comprising the history of the
young of man and animals, and it may be also of plants. The term is derived from the Greek
ov, signifying a growing part or thing, and has been somewhat vaguely applied to the product of
generation of any plant or animal which is in process of formation. Among the higher animals,
and especially in the human species, the Latin word foetus has sometimes been employed in the
same signification as embryo, but it is more generally held to denote a more advanced stage of
formation, while the term embryo is applied to the earlier condition of the product of
conceptionbefore it has assumed the characteristic form and structure of the parent.

In all animals, with the exception of the Protozoa, the new being, deriving its
origin from a definite organized structure termed the ovum or egg, passes during the progress of
its formation and growth from a simpler to a more complex form and organic structure by a
series of consecutive changes which come under the general denomination of development. The
consideration of these changes, which is mainly an anatomical subject, being partly
morphological as affecting the larger and more obvious organic form, and partly biological as
belonging to the minute or textural structure, constitutes by far the greater part of the science of
embryology, but the latter word may also include the history of all other living phenomena
manifested by the young animal in the progress of its growth to maturity.

The formative process through which the embryo passes is necessarily of very
different degrees of complexity, according to the more simple or complex
organization of the adult animal to which it belongs. But it presents throughout
the whole range of animals certain general features of similarity dependent on
the fundamental resemblance of the organized elements from which all animals
derive their origin.

A minute mass of protoplasm constitutes not only the simplest, but also the
invariable, form presented by the germinal part of the ovum or egg, and in all
animals, except the Protozoa, in which the nature of the germ is still doubtful, it
takes at first the form of an organized cell, or it is a definite spherical and
nucleated mass of protoplasm. It is therefore a germ-cell.

In all ova the first stage of the formative process, following upon fecundation of
the germ, consists in the multiplication of the egg or germ-cell by a process of
the nature of fissiparous division, so that when this division has proceeded some
length, it results in the production of a mass or congeries of organized cells
descended from that which formed the primitive germ, and containing in
combination the molecular elements of the materials contributed by the male
and female parents to the formation of the fertilized germ. This is the mulberry
stage, or morula, of Haeckel. In a more advanced stage among the higher
animals, the ells of this mass assume more or less of a laminar arrangement
constituting the blastoderm or germinal membrane of Pander and succeeding
authors; and in the first and lowest forms of this structure two layers are
distinguished, corresponding to the outer and inner cellular laminae of which
the earliest form of the embryo consists in the higher, and the whole of the body
in the lower, forms of animals. These layers are the ectoderm and endoderm of
the embryologist and comparative anatomist (Huxley and Allman).

In the lowest animals little if any farther differentiation of the germinal
structures ensues; but in animals higher in the scale there arises a third or
intermediate layer, the mesoderm, which takes an important part along with the
other two layers in the formation of the animal organism. The cellular
blastoderm, therefore, is already the embryo of the lowest animals; while in the
higher that term could scarcely with propriety be applied to the product of
development in the egg until some of the characteristic lineaments, however
rudimentary, of the new animal are apparent.

But in the whole of this process of embryonic development, whether it be of the
simplest or of the most complex kind, it is to be observed that it is solely by the
multiplication and differentiation of cells which have descended more or less
directly from the original germ-cell that the organizing process is effected. It
follows from this that the processes of organic growth or embryonic
development present a textural or histological uniformity to a remarkable
degree throughout the whole zoological series. There is also a very striking
similarity in the morphological phenomena of development within large groups
of animals. Our knowledge, indeed, of the mode of formation of the young in all
the varied forms of animal organization is still too limited to admit of our
affirming that a uniform and progressive morphological type pervades the whole
animal kingdom; but already many ascertained facts point strongly to such a
conclusion, and the more our knowledge of the process of development in
individual animals (ontogeny ) advances, the greater resemblance do we
recognize in the formative processes; so that it becomes more and more
probable that the morphological development of any of the higher animals
includes, or as it were repeats within certain limits, the various steps of the
process which belong to the inferior grades of the animal kingdom. Hence we
are led to the further conclusion that there is an essential correspondence
between the individual development or ontogeny of the higher animals and the
progressive advance of the organization in the whole animal series.

If, further, we adopt the Darwinian view of the evolution of animal life and
organization by descent of one species of animals from others preceding it, we
shall see that the embryological history of any animal is at the same time the
history of its relation to other animals and of its phylogenetic development or
gradual derivation as a species from more simple progenitors in the lapse of
time. It is obvious, therefore, that we must look to the future progress of
embryology as well as of palaeontology for a large portion of the facts upon
which the confirmation of the modern theory of evolution will rest.

From what has been said it will be apparent that it would be impossible, within
the limits of one article, to trace even in the briefest possible manner the
phenomena of embryological development in all different animals. But special
descriptions, so far as required, will find their appropriate places under the
divisions of animals to which they respectively belong; and as there are some
considerations relating to embryology which require to be stated besides the
history of development, it has been deemed advisable to bring the more
important facts of develop meat of the embryo into connection with those
relating to reproduction in general under the heading GENERATION, to which
article, therefore the reader is referred.

In the present article, accordingly, we shall do no more than trace shortly the
steps by which the modern science of Embryology has originated and has
assumed the important position which it now occupies among the biological
sciences.

In its scientific and systematic form embryology may be considered as having
only taken birth within the present century, although the germ from which it
sprung was already formed nearly half a century earlier. The ancients, it is true,
as we see by the writings of Aristotle and Galen, pursued the subject with
interest, and the indefatigable Grecian naturalist and philosopher had even
made continued series of observations on the progressive stages of development
in the incubated egg, and on the reproduction of various animals; but although,
after the revival of learning, various anatomists and physiologists from time to
time made contributions to the knowledge of the foetal structure in its larger
organs, yet from the minuteness of the observations required for embryological
research, it was not till the microscope came into use for the investigation of
organic structure that any intimate knowledge was attained of the nature of
organogenesis. It is not to be wondered at, therefore, that during a long period,
in this as in other branches of physical inquiry, vague speculations took the
place of direct observation and more solid information. This is apparent in most
of the works treating of generation during the 16th and part of the 17th
centuries. (1.)

Harvey was the first to give, in the middle of the latter century, a new life and
direction to investigation of this subject, by his. discovery of the connection
between the cicatricula of the yolk and the rudiments of the chick, and by his
faithful description of the successive stages of development as observed in the
incubated egg, as well as of the progress of gestation in some Mammalia. Hehad
also the merit of fixing the attention of physiologists upon general laws of
development as deduced from actual observation of the phenomena, by the
enunciation of two important propositions, viz.~(l) that all animals are produced
out of ova, and (2) that the organs of the embryo arise by new formation, or
epigenesis, and not by mere enlargement out of a pro-existing invisible condition
(Exercitationes de Generatione Animalium', Amstelodami, 1651, and in English
by G. Ent,

1853, London). Harvey's observations, however, were aided only by the use of
magnifying glasses (perspecillie), probably of no great power, and be saw
nothing of the earliest appearances of the embryo in the first thirty-six hours,
and believed the blood and the heart to be the parts first formed.

The influence of the work of Harvey, and of the successful application of the
microscope to embryological investigation, was soon afterwards apparent in the
admirable researches of Malpighi

of Bologna, as evinced by his communications to the Royal Society of London in
1672, '~ De

( 1. It may be proper to mention, as authors of this period who made special
researches on the development of the embryo (1) Voicher Coiter of Groningen,
who, along with Aidrovandus of Bologna, made a series of observations on the
formation of the chick, day by day, in the incubated egg, which were described
in a work published in 1573, and (2) Hieronymus Fabricias (ab
Aquapendente),who by many fine engravings, of uterogestation and the foetus of
a number of quadrupeds and other animals, and in a posthumous work entitled
De formatione ovi et pulli, edited by J. Prevost, and published at Padua in 1621,
described and illustrated by engravings the daily changes of .the egg in
incubation. It is enough, however, to say that Fabricius was entirely ignorant of
the earlier phenomena of development which occur in the first two orthree days,
and even of the Source of the embryonic rudiments, which he conceived to
spring, not from the yolk or true ovum, but from the chalazae or twisted deepest
part of the white. The cicatricula he looked upon as merely the vestige of the
pedicle by which the yoke had been previously attached to the ovar ).

ovo incubato," and "De formatione pulli," and more especially in his
delineations of some of the earlier phenomena of development, in which, as in
many other parts of minute anatomy, he partially or wholly anticipated
discoveries, the full development of which has only been accomplished in the
present century. Malpighi traced the origin of the embryo almost to its very
commencement in the formation of the cerebro-spinal groove within the
cicatricula, which he removed from the opaque mass of the yolk; and he only
erred in supposing the embryonal rudiments to have pre-existed as such in the
egg, in consequence, apparently, of his having employed for observation, in very
warm weather, eggs which, though he believed them to be unincubated, had in
reality undergone some of the earlier developmental changes.

The works of Walter Needham (1667), Regner de Graaf (1673), Swammerdam
(1685), Vallisneri (1689)~following upon those of Harvey- all contain
important contributions to the knowledge of our subject, as tending to show the
similarity in the mode of production from ova in variety of animals with that
previously best known in birds. The observations more especially of De Graaf,
Nicolas Steno, and J. van Home gave much greater precision to the knowledge
of the connection between the origin of the ovum of quadrupeds and the vesicles
of the ovary now termed Granflan, which. De Graaf showed always burst and
discharged their contents on the occurrence of pregnancy.

These observations bring us to the period of Boerhaave and Albinus in the
earlier part of the 18th century, and in the succeeding years to that of Haller,
whose vast erudition and varied and animals, and the succeeding ro that of
Haller, whose vast erudition and varied and accurate original observations
threw light upon the entire reproduction in animals, and brought its history into
a more systematic and intelligible form. A considerable part of the seventh and
the whole of the eighth volumes of Haller's great work, the Elementa Physiogia,
published at successive times from 1757 to 1766, are occupied with the general
view of the function of generation, while his special contributions to embryology
are contained in his Deux Memoires sur la formation de Coeur dans le Pouet,
and Deux Memoires sur la formation des Os, both published at Lausanne in
1758, and republished in an extended and altered form, together with his
"Observations on the early condition of the embryo in Quadrupeds,". made
along with Kuhlemann, in the Opera Minora (1762-68). Though originally
educated as a believer in the doctrine of "pro-formation" by his teacher
Boehaave, Haller was Soon led to abandon that view in favour "epigenesis" or
new formation, as may be seen in various parts of his works published before the
middle of the century see especially a long note explanatory of the grounds of
his change of Opinion in his edition of Boerhaave's Praelections Academicae
vol. v. part 2, p 497 (1744), and his Primae Lineoe Psysiologioe (1747). But
some years later, and after having been engaged in observing the phenomena of
development in the incubated egg, he again changed his views, and during the
remainder of his life Was a keen Opponent of the system of epigonosis and a
defender and exponent of the theory of "evolution." as it was then named~ a
theory very different from that now bearing the name, and which implied belief
in the pre-existence of the organs of the embryo in the. germ, according to the
theory of encasement (emboitement) or inclusion supported by Leibnitz and
Bonnet. (See the interesting work of Bonnet, Considerations sur les Corps
Organises, Amsterdam, 1762, for an account of his own views and those of
Haller.) The reader is also referred to the article Evolution in the present
volume, for a further history of the change which has taken place in the use of
the term in more recent times. (Note: The Evolution topic is approximately 30
pages long.)

It was reserved for Caspar Frederick Wolff (1733-1794), a German by birth, but
naturalized afterwards in Russia, to bring forward observations which, though
almost entirely neglected for a long time after their publication, and in some
measure discredited under the influence of Haller's authority, were sixty years
later acknowledged to have established the theory of epigenesis upon the secure
basis of ascertained facts, and to have laid the first foundation of the
morphological science of embryology. Wolff'S work, entitled Theoria
Generationis, first published as an inaugural Dissertation at Berlin in 1759, was
republished with additions in German at Berlin in 1764, and again in Latin at
Halles in 1774. Wolff also wrote a "Memoir on the Development of the
Intestine" in Nov. Comment. Acad. Petrocol., 1768 and 1769. But it was not till
the latter work was translated into German by J. F. Meckel, and appeared in his
Archiv for 1812, that Wolff's peculiar merits as the founder of modern
embryology came to be known or fully appreciated.

The special novelty of Wolff's discoveries consisted niamly in this, that
heshowed that the germinal part of the bird's egg forms a layer of united
granules or organized particles (cells of the modern histologist), presenting at
first no semblance of the form or structure of the future embryo, but gradually
converted by various morphological changes in the formative material, which
are all capable of being trace& by observation, into the several rudimentary
organs and systems of the embyro. The earlier form of the embryo he delineated
with accuracy; the actual mode of formation he traced in more than one organ,
as for example in the alimentary canal, and he was the discoverer of several new
and important embryological facts, as in the instance of the primordial kidneys,
which have thus been named the Wolffian bodies. Wolff further showed that the
growing parts of plants owe their origin to organized particles or cells, so that
he was led to the great generalization that the processes of embryonic formation
and of adult growth and nutrition are all of a like nature in both plants and
animals. No advance, however, was made upon the basis of Wolff's discoveries
till the year 1817, when the researches of Pander on the development of the
chick gave a fuller and more exact view of the phenomena less clearly indicated
by Wolff, and laid down with greater precision n plan of the formation of parts
in the embryo of birds, which may be regarded as the foundation of the views of
all subsequent embryologists.

But although the minuter investigation of the nature and true theory of the
process of embryonic development was thus held in abeyance for more than half
a century, the interval was not unproductive of observations having an
important bearing on the knowledge of the anatomy of the foetus and the
function of reproduction. The great work of William Hunter on the human
gravid uterus, containing unequalled pictorial illustrations of its subject from
the pencil of Ryinsdyk and other artists, was published in 1775,1 and during a
large part of the same period numerous communications to the Memoirs of the
Royal Society testified to the activity and genius of his brother, John Hunter, in
the investigation of various parts of comparative embryology. But it is mainly in
his rich museum, and in the manuscripts end drawings which he left, and which
have been in part described and published in the catalogue of his wonderful
collection, that we obtain any adequate idea of the unexampled. industry and
wide scope of research of that great anatomist and physiologist.

As belonging to a somewhat later period, but still before the time when the more
strict investigation of embryological

1(Along with the work of W Hunter must be mentioned a large collection or
unpublished observations by Dr James Douglas, which are preserved in the
Hunterian Museum of G1asgow University.)

phenomena was resumed by Pander, there fall to be noticed, as indicative of the
rapid

progress that was making, the experiments of Spallanzani, 1789; the researches
of Autenrieth, 1797, and of Soemmering, 1799, on the human foetus; the
observations of Senff on the formation of the skeleton,~1801; those of Oken and
Kieser on the intestine and other organs, 1806; Oken's remarkable work on the
bones of the head, 1807 (with the views promulgated in which Goethe's name is
also intimately connected); J. F. Mecke1's numerous and valuable contributions
to embryology and comparative anatomy, extending over a long series of years;
and Tiedemann's classical work on the development of the brain, 1816.

Christian Pander's observations were made at the instance and under the
immediate supervision of Prof. Döllinger at Wurzburg, and we learn from Von
Baer's autobiography that he, being an early friend of Pander's, and knowing
his qualifications for the task, had pointed him out to Döllinger as well fitted to
carry out the Investigation of development which that professor was desirous of
having accomplished. Pander's inaugural dissertation was entitled Historia
metamorphoseos quan ovun incubatum prioiubus quinque diebus
subit,Virceburgi, 1817; and it was also published in German under the title of
Beiträge zur Entwickelungeschichte des hühnchens im Eie, Würzburg, 1817.
The beautiful plates illustrating the latter work were executed by the elder
D'Alton, well known for his skill in scientific observation, delineation, and
engraving.

Pander observed the blastoderm or germinal membrane of the fowl's egg to
acquire three layers of organized sub-stance in the earlier period of incubation.
These he named respectively the serous or outer, the vascular or middle, and the
mucous or inner layers; and he traced with great skill and care the origin of the
principal rudimentary organs and systems from different ones of these layers,
pointing out shortly, but much more distinctly than Wolff had done, the actual
nature of the changes occurring in the process of development.

Carl Ernest von Baer, the greatest of modern embryologists, was, as already
remarked, the early friend of Pander, and, at the time when the latter was
engaged in his researches at Würzburg, was associated with Döllinger as
prosector, and engaged with him in the study of comparative anatomy. He
witnessed, therefore, though he did not actually take part in, Pander's
researches; and the latter having afterwards abandoned the inquiry, Von Baer
took it up for himself in the year 1819, when he had obtained an appointment in
the university of Königsberg, where he was he colleague of Burdach and Rathke,
both of whom were able coadjutors in the investigation of the subject of his
choice. (See V. Baer's interesting autobiography, published on his retirement
from St Petersburg to Dorpat in 1864.)2.

Von Baer's observations were carried on at various times from 1819 to 1826
and 1827, when he published the first results in a description of the development
of the chick in the first edition of Burdach's Physiology.

It was at this time that Von Baer made the important discovery of the ovarian
ovum of mammals and of man, totally unknown before his time, and was thus
able to prove as matter of exact observation what had only been surmised
previously, viz., the entire similarity in the mode of origin of these animals with
others lower in the scale. Epistola de Ovi Mammalium det Hominis eGensei,
Lipsia~, 1827. See

(2. Von Baer was born in the Russian province of Esthonia in 1792, and was
educated at Dorpat and in Gernany. After having been fifteen years professor in
the Prussian university of Königsberg, he was called to St Petersburg, where he
remained for nearly thirty years, and, as professor and member of the imperial
Academy, promoted in the most zealous and able manner, by his unexampled
activity, comprehensive and original views, sound judgment, and powerful
co-operation, the whole range of scientific education and biological research.)

166

also the interesting commentary on or supplement to the Epistola in Heusinger's
Journal, and the translation in Bresehet's Répertore, Paris, 1829.)

In 1829 Von Baer published the first part of his great work, entitled
Beobuchtungen und Reflexionen uber de Entwickelungsgeschichte der Thiere
the second part of which, still leaving the work incomplete, did not appear till
1838. In this work, distinguished by the fulness, richness, and extreme accuracy
of the observations and descriptions, as well as by the breadth and soundness of
the general views on embryology and allied branches of biology which it
presents, he gave a detailed account not only of the whole progress of
development of the chick as observed day by day during the incubation of the
egg, but he also described what was known, and what he himself had
investigated by numerous and varied observations, of the whole course of
formation of the young in other vertebrate animals. His work is in fact a system
of comparative embryology, replete with new discoveries in almost every part.

Von Baer's account of the layers of the blastoderm differs somewhat from that
of Pander, and appears to be more consistent with the further researches which
have lately been made than was at one time supposed, in this respect, that he
distinguished from a very early period two primitive or fundamental layers, viz.,
the animal or upper, and the vegetative or lower, from each of which, in
connection with two intermediate layers derived from them, the fundamental
organs and systems of the embryo are derived:- the animal layer, with its
derivative, supplying the dermal, neural, osseous, and muscular; the vegetative
layer, with its derivative, the vascular and mucous (intestinal) systems. He laid
down the general morphological principle that the fundamental organs have
essentially the shape of tubular cavities, as appears in the first form of the
central organ of the nervous system, in the two muscular and osseous tubes
which form the walls of the body, arid in the intestinal canal; and he followed
out with admirable clearness the steps by which from these fundamental systems
the other organs arise secondarily, such as the organs of sense, the glands,
lungs, heart, vascular glands, Wolffian bodies, kidneys, and generative organs.

To complete Von Baer's system there was mainly wanting a more minute
knowledge of the intimate structure of the elementary textures, but this had not
yet beau acquired by biologists, and it remained for Thomas Schwann of Liege
in 1839, along with whom should be mentioned those who, like Robert Brown
and Schleiden, prepared the way for his great discovery, to point out the
uniformity in histological structure of the simpler forms of plants and animals,
the nature of the organized animal and vegetable cell, the cellular constitution
of the primitive ovum of animals, mid the derivation of the various textures,
complex as well as simple, from the transformation or, as it is now called,
differentiation of simple cellular elements, discoveries which have exercised a
powerful and lasting influence on the whole progress of biological knowledge in
our time, and have contributed in an eminent degree to promote the advance of
embryology itself.

To Reichert of Berlin more particularly is due the first application of the newer
histological views to the explanation of the phenomena of development, 1840.
To him and to Kölliker and Virchow is due the ascertainment of the general
principle that there is no free-cell formation in embryonic development and
growth, but that all organs are derived from the multiplication, combination,
and transformation of cells, and that all cells giving rise to organs are the
descendants or progeny of previously existing cells, and that these may be traced
back to the original cell or cell-substance of the ovum.

It may be that modern research has somewhat modified the views taken by
biologists of the statements of Schwann as to the constitution of the organized
cell ~ especially as regards its simplest or most elementary form and has
indicated more exactly the nature of the protoplasmic material which constitutes
its living basis; but it has not caused any very wide departure from the general
principles enunciated by that physiologist. Schwann's treatise entitled
Miscrocopical Researches into the Accordance in the Structure and Growth of
Animals and Plants, was published in German at Berlin in 1839, and was
translated into English by Henry Smith, and printed for the Sydenham Society in
1847, along with a translation of Schleiden's memoir, " Contributions to
Phytogenesis," which originally appeared in 1838 in Müller's Archiv for that
year, and which had also been published in English in Taylor and Francis's
Scientific Memoirs, vol. ii. part vi.

Among the newer observations of the same period which contributed to a more
exact knowledge of the structure of the ovum itself may he mentioned-first, the
discovery of the germinal vesicle, or nucleus, in the germ disk of birds by
Purkinjo (Syboloe ad ovi avium historiam ante incubationem, Vratislaviae,
1825, and republished at Leipsic in 1830); second, Von Paer's discoverv of the
mammiferous ovum in 1827, already referred to third thediscovery of the
germinal vesicle of mammals by Cost in 1834, and its independent observation
by Wharton Jones in 1835; and fourth, the observation in the same year by
Rudolph Wagner of the germinal macula or nucleus Coste's discovery of the
germinal vesicle of Mammalia was first communicated to the public in the
Comtes Rendus of the French Academy for 1833, and was more fully described
in the Recherches sur la génération des Mammiféres, by Delpech and Coste,
Paris, 1834. Thomas Wharton Jones's observations, made in the autumn of
1834, without a knowledge of Coste's communication, were presented to the
Royal Society in 1835. This discovery was also confirmed and extended by
Yalentin and Bernardt, as recorded bv the latter in his work Symb. ad ovi
Mammal. Hist.t ante proegnationem. Rudolph Wagner's observations first
appeared in his Textbook of Comparative Anatomy, published at Leipsic in
1834-5, and in MülIer's Archiv for the latter year. His more extended
researches are described in his work Prodromus hist. generationis hominis
atque animalium Leipsic, 1836, and in a memoir inserted in the Trans. of the
Roy Bavarian Acad. Of Sciences, Munich, 1804

The two decades of years from 1820 to 1840 were peculiarly fertile in
contributions to the anatomy of the foetus and the progress of embryological
knowledge. The researches of Prevost and Dumas on the ova mid primary
stages of development of Batrachia, birds, and mammals, made as early as
1824, deserve especial notice as important steps in advance, both in the
discovery of the process of yolk segmentation in the batrachian ovum, and in
their having shown almost with the force of demonstration, previous to the
discovery of the mammiferous ovarian ovum by Von Baer, that body must exist
as a minute spherule in the Graefian follicle of the ovary, although they did not
actually succeed in bringing the ova clearly under observation.

The works of Pockels (1825), of Seiler (1831), of Bresebet (1832), of Velpeau
(1833), of Bisehoff (1834)-all bearing upon human embryology; the researches
of Coste in comparative embryology in 1834, already referred to, and those
published by the same author in 1837; the publication of Joannes Müller's great
work on physiology, and Rudolph Wagner's smaller text-book, in both of which
the subject of embryology received a very full treatment, together with the
excellent Manual of the Development of the Foetus, by Valentin, in 1835, the
first separate and systematic work on the whole subject, now secured to
embryology its permanent place among tbe biological sciences on the Continent;
while in this country attention was drawn to the subject by the memoirs of Allen
Thomson (1831), Th. Wharton Jones (1835-38) and Martin Barry (1839-40).

Among the more remarkable special discoveries which belong to the period now
referred to, a few may be mentioned, as, for example, that of the chorda dorsalis
by Von Baer, a most important one, which may be regarded as the key to the
whole of vertebral morphology; the phenomenon of yolk segmentation, now
known to be universal among animals, but which was only first carefully
observed in Batrachia by Prévost and Dumas (though previously casually
noticed by Swammerdam), and was soon afterwards followed out by Rusconi
and Von Baer in fishes ; the discovery of the branchial clefts, plates, and
vascular arches in the embryoes of the higher abranchiate animals by Rathke in
1825-27; the able investigation of the transformations of these arches by
Beichert in 1837; and the researches on the origin and development of the
urinary and generative organs by Joannes Müller in 1829-30.

On entering the fifth decade of our century, the number of original
contributions and systematic treatises becomes so great as to render the attempt
to enumerate even a selection of the more important of them quite unsuitable to
the limits of the present article. We must be satisfied, therefore, with a reference
to one or two which seem to stand out with greater prominence than the rest as
land-marks in the progress of embryological discovery. Among these may first
be mentioned the researches of Theodor F. W. von Bischoff, formerly of Giessen
and now of Munich, on the development of the ovum in Mammalia, in which a
series of the most laborious, minute, and accurate observations furnished a
greatly novel and very full history of the formative process in several animals of
that class. These researches are contained in four memoirs, treating separately
of the development of the rabbit, the dog, the guinea-pig and the roe-deer, and
appeared in succession in the years 1842, 1845, 1852, and 1854.

Next may be mentioned the great work of Coste, entitled Histoire gén. particul.
du Developpement des Animaux,of which, however, only four fasciculi appeared
between the years 1847 and 1859, leaving the work incomplete. In this work; in
the large folio form, beautiful representations are given of the author's valuable
observations on human embryology, and on that of various mammals, birds, and
fishes, and of the author's discovery in 1847 of the process of partial yolk
segmentation in the germinal disc of the fowl's egg during its descent through
the oviduct, and his observations on the same phenomenon in fishes and
mammals.

The development of reptiles received important elucidation from the researches
of Rathke, in his history of the development of serpents, published at Königsberg
in 1839, and in a similar work on the turtle in 1848, as well as in a later one on
the crocodile in l866,~along with which may be associated the observations of
H. J. Clark on the "Embryology of the Turtle," published in Agassiz's
Contributions to Natural History, &c., 1857.

The phenomena of yolk segmentation, to which reference has more than once
been made, and to which later researches give more and more importance in
connection with the fundamental phenomena of development, received great
elucidation during this period, first from the observations of C. T. E. von Siebold
and those of Bagge on the complete yolk segmentation of the egg in nematoid
worms in 1841, and more fully by the observations of Kölliker in the same
animals in 1843. The nature of partial segmentation of the yolk was first made
known

167

by KölIiker in his work on the development of the Cephalopoda in 1844, and, as
has already been mentioned, the phenomena were observed by Coste in the eggs
of birds. The latter observations have since been confirmed by those of
Oellacher, Götte, and Ködlliker. Further researches in a vast number of
animals give every reason to believe that the phenomenon of segmentation is in
some shape or other the invariable precursor of embryonic formation.

A large body of facts having by this time been ascertained with respect to the
more obvious processes of development, a further attempt to refer the
phenomena of organogenesis to morphological and histological principles
became desirable. More especially was the need felt to point out with greater
minuteness and accuracy the relation in which the origin of the fundamental
organs of the embryo stands to the layers of the blastoderm; and this we find
accomplished with signal success in the researches of Remak on the
development of the chick and frog, published between the years 1850 and 1855.

From Remak's observations it appeared that the middle layer of the blastoderm,
whatever may be the precise source from which it originally springs,-a point left
undetermined by Von Baer, Remak, and even by more recent observers,
-becomes divided in its lateral portions into two laminae, so as to leave between
them the cavity which afterwards intervenes between the external wall and the
contained viscera of the body. This cavity corresponds to the pleuro-peritoneal
space of the higher animals, and may be designated in the lower by the general
term of coelom (Haeckel).

While, therefore, Remak recognized an outer and an inner layer of the
blastoderm, corresponding only in some measure with the serous and mucous
layers of Pander, he showed that the greater part of the middle layer is divided
into two, the outer of which is the main source of the osseous and muscular
walls of the body, and the inner is the seat of development of the involuntary
contractile walls of the alimentary canal, the heart, and the principal vessels.

Thus, according to the system of Remak, while the central portion of the middle
layer remains undivided, and gives rise to the axial chorda dorsalis or
notochord, with the surrounding vertebral arid cranial walls, the lateral parts of
this layer are in the earlier stage of its development split into two by the
formation of the pleuroperitoneal cavity, and there thus result the four layers
whose relation may, according to the light received from more recent inquiry, be
tabularly represented as follows

Primitive .... Ectoderm I. Sensorial or Epiblast. .

2. Body WalI. Secondary

B1astoderm....Endoderm 2. 3. Mesoderm or Mesoblast..

3. Viseral Wall Blastoderm

4.Intestinal or Hypoblast

From the first of these layers (1), the neuro-corneous of Remak, now named
epiblast, the cuticular system and central organs of the nervous system
(cerebro-spinal axis) are primarily formed, and secondarily, certain parts of the
principal organs of sense, viz., the eye, ear, and nose. The motoro-germinative
is the name applied to the middle layer by Remak, of which (2), the outer
division, the volunto-motory, corresponding to the body-wall or somatopleure of
more recent authors, furnishes the material for the development of the true skin,
the voluntary muscles, and the skeleton; and (3), the inner division, the
involunto-motorv, corresponding to the visceral wall or splanchno-pleure of
recent authors, is the source of formation of the contractile wall of the
alimentary canal, the heart, and larger blood-vessels, the vascular glands, the
primordial kidneys, and the generative organs. The fourth or lowest layer (4),
the intestino-glandular of Remak and the hypoblast of recent writers, is the
source of the epithelial lining of the alimentary canal and air passages and of
the cellu]ar parts of the internal glands.

These researches of Remak appear in some measure to reconcile the views of
Von Baer with those of other embryologists, as to the constitution of the
blastoderm and the relation of its several layers to the fundamental systems and
organs of the embryo. Recent observation, though modifying them in some
respects, has not led to any important invalidation of their general results; and
we may therefore in the meantime regard them as forming the principal basis or
starting-point of modern embryological inquiries, although much still remains to
be ascertained as to the source of the mesoblast and its relation to the two
primitive layers of the blastoderm. More especially important in a comparative
embryological view is the formation of the coelom or somato-visceral cavity, as
connected with the gradual appearance in the animal series of the lymphatic and
blood vascular cavities.

But while the researches of Remak and others had thus in the commencement of
the sixth decade of our century brought the history of the general phenomena of
development or embryogeny into a consistent and systematic form, especially as
known in the higher vertebrates, much still remained to be done in the more
minute investigation of the origin of the ovum and its germ, and the intimate
nature of the process of fecundation, as well as iti regard to the histological and
morphological changes in which the organogenic processes consist. The
progress of discovery in these departments has been greatly promoted by the
very great improvements which have been introduced into the methods of
investigation, the successful prosecution of which has had an equally favourable
influence on the whole range of minute anatomy and histology, viz.-(l), the
hardening, clearing, and tinting processes of preparation; (2), the method of fine
section of the parts to be observed; and (3), the permanent preservation of
specimens in the moist or dried state.

The first of these methods may be said to have had its origin in the introduction
of the use of chromic acid as a hardening agent by Hannover of Copenhagen in
1840; and the works on practical histology since published bear ample
testimony to the prodigious advance in refinement in the adaptation of this and
other methods of hardening and distinctive coloration of the tissues, which have
in recent times rendered the minuter investigation of the tissues comparatively
elegant and exact, and indeed now almost exhaustive.

The second method, or that of sections, as applied to embryological research,
obviously suggested by the diagrams of Pander and Von Baer, seems first to
have been practically applied by Allen Thomson in 1831, though without the
assistance of finer modern appliances, in the ascertainment of the earliest
double condition of the aorta in the bird's embryo. Jt was soon carried to a
much greater extent by Reichert, and later by Remak, and it is now universally
pursued as a principal means of embryological investigation. To show the
extent to which the successful combination of the above-mentioned methods is
now carried by the use of the most approved chemical reagents and the best
sectional instruments, it may be stated that as many as several hundreds of
perfectly clear sections may be made through the body of an embryo of only half
an inch in length, and that similarly thin sections may be made in any desired
direction through the smallest as well as larger ova, and that, notwithstanding
the extreme delicacy of some of the parts and the inequality of their density,
every one of the sections may be made to present a distinct and true view both of
the microscopic histological characters and of the larger morphological
relations of the parts observed.

Accordingly, during the time which has elapsed since the publication of
Remak's work, the number of contributions

to different parts of our subject, by the history of original observations made
mainly by the way of sections has been immense, and it goes on increasing to
the present time. Among the more important of these, as influencing the general
progress of embryological science, the following may be mentioned.

First, in connection with the development of Fishes, the researches of
Lerehoullet "On the Pike and the Perch" (Annal. des Sciences Nat., 1862,);
those of Joseph Oellacher On the Trout" (Zei1sch. für Wisseisch. Zool., 1872);
those of his. also "On Osseous Fishes," appearing in 1875, and the important
and elaborate researches of . F.M. Balfour "On the Elastmobranch of Fishes,"
in 1874 mid following years (Journ. of Anat. and Physiol. and Quart. Journal of
Microscopic Anatomy); the prize memoir, of Max Schulze On the Development
of the River Lamprey Haarlem, 1856 ; and the researches of Kowalewsky "On
the Development of the Amphioxus" (in the Mem. of St Petersburg Acad.1867),
are deserving of notice.

Second, in regard to Amphibia, after the memoirs of Rusconi Reichert, Remak,
and C. Vogt of earlier date, the most important recent contributions are those of
Y. Bambecke " On tlsc develop- ment of Pelobates fuscus" (Mém. de l'Acad. de.
Belgique vol xxxiv., 1868), and the very beautiful work of C. Cötte On the
Development of the Toad, Bombinator igneus(Leipsic, 1874 folio).

Third, in regard to Reptilia, not much has been done since Rathke's work On
the Development of the Turtle was published in 1848. But there may be
mentioned as valuable contributions to this department, the Account of the
Development of the Crocodile by Rathke himself in 1866, and the "Embryology
of the Turtle by H. J..Clark, in Agassiz's Contributions to the Natural History of
the United States (vol. ii. 1857).

Fourth, in the class of Birds, the most notable work which has appeared in
recent times on the earlier phenomena of their development is that of His,
entitled Researches on the Firsl Foundation of the Body in Vertebrate Animals
(Leipsic, 1868), in which a careful revision of the subject is undertaken from
original observations, and a clearer distinction established between the axial or
central and the lateral parts of the blastoderm. Under this head come also the
researches of Dursy upon the primitive trace of the chick (Lahr, 1866) F M
Balfour's paper on the same subject (1873) and the important observations of
Peremeschko on tle formation of the layers of the Bastoderm, especially the
middle of (Vienna Acad., 1868), Affanasieff on the first circulation in the fowl's
embryo (in 1866), E. Klein on the development of blood vessels and blood
corpuscles from the middle layer (1868), along with which may also be quoted
the observations of Waldeyer, Ocllacher, Stricker, Götte, Balfour, and Kölliker
as tending to throw light on the origin of the blastodermic layers.

Fifth, in regard to Mammalia, the most recent observations after those of
Bischoff on the process of development in this class are those of Hensen, in
Zeitsch für Anat. und Entwiekelungsgesch vol. i., 1875-6 ; the observations of
Kölliker in the new edition of his systematic work, 1876 ; those of Reichert, in
his Account of the Development of the Guineapig, Berlin, 1862, and his
Description of an Early Human Product, &c., Berlin, 1873 also in the papers of
E. A. Schafer, from Physiol. Laborat. Univ. Coll. London and Proceedings Roy.
Soc., 1876.

On the structure and morphology of the ovum may be quoted the article "Ovum"
in the Cyclopedia of Anatomy and Physiology, by Allen Thomson (1852-56); the
contributions of Gegenbaur 186l and 1864, and of Cramer, 1868 ; and the very
able 'Mémoire Couronné" of Edward van Beneden, Recherches sur la
composition et la signification de l'Oeuf, Brussels, 1870.

With respect to the process of segmentation of the ovum and earliest steps in the
formation of the germ, the most interesting researches have recently been
communicated by Auerbach, Butschli, Strasburger, Edw. van Beneden, Oscar
Hertwig, and others, which are still in progress, and will be referred to in the
article GENERATION.

Several systematic works or text-books on embryology have appeared since it
assumed the form and dimensions of a special branch of science. The first of
these, by Valentin, referring to the deve1opment of man, mammals, and birds,
was published in 1835. The next was that of Bischoff, published in 1842, as one
of the volumes of the encyclopedic system of anatomy named after Soemmering.
The third work of this kind was that of Kölliker, in the form of lectures,
published in 1861, and giving a very full account of the development of the ovum
and embryo in man and the higher animals. Of this work a second edition is
now in progress, the first part having appeared in 1876. To this excellent work,
as the production of one who has contributed a very large amount of original
observations on embryology and the whole range of minute anatomy, the reader
may he referred for the fullest aud most accurate systematic information on the
subject. In comparative embryology we have the interesting short treatise of
Rathke, edited after his death by Kölliker in 1861, and the Lehrbuch der
Vergleichende Embryologie by S. L. Schenk, Vienna, 1874 We may also refer
here to the excellent plates illustrating embryology in the Icones physiologicoe
of A. Ecker, 1854.

In this country, since the appearance of the very careful translation of Müller's
Physiology by Baly, which had the advantage of revision in many of its parts by
Sharpey, and the translation of Wagner's Physiology in 1846, there has
appeared only one systematic work on embryology, viz., the Elements of
Embryology by M. Foster and F. M. Balfour, of which the first part, which
appeared in 1874, treating of the development of the embryo of bird deserves the
highest praise. A short view of human embryology is given hy Allen Thomson in
the 8th edition of Quain's

Anatomy, 1876

For an account of the relation of embryology to the classification of animals
and to phylogeny or the theory of descent, the English reader is referred to
various parts of the writings of Darwin and Huxley, and to the excellent
translation of Haeckel's work on the History of Creation, 2 vols., London, 1874;
to F. M. Balfours "Comparison of the Early Stages in the Development of
Vertebrates" in Journ. of Microscopical Science, vol. xv., 1875, and to the
recently published Notes on Embryology and Classification, by B. Ray
Lankester, 1877.

In the preceding sketch of the history of the foundation and progress of the
science of embryology, no attempt has been made to trace that part of it which
includes the development of different invertebrate animals, as it was felt that
from the extremely numerous, varied, scattered, and fragmentary nature of many
of the contributions of authors in this part of our subject, any attempt at the
citation even of the more important would be quite unsuitable to this work.

It will be enough for us here to state that the first considerable original work on
the development of a division of the invertebrates was that of Maurice Herold of
Marburg on spiders, "De generatione Aranearum ex ovo," published at Marburg
in 1824, in which the whole phenomena of the formative process in that animal
are described with remarkable clearness and completeness.

A few years later an important series of contributions to the history of the
development of invertebrate animals appeared in the second volume of Burdachs
work on Physiology of which the first edition was published in 1828, and in this
the history of the development of the Entozoa was the production of Ch.. Theod.
Von Siebold, and that of most of the other invertebrates, was compiled by Rathke
from the results of his own observations and those of others. These memoirs,
together with others subsequently published by Rathke, entitle him to be
regarded as the founder of invertebrate embryology.

It would be quite unsuitable in this article to attempt to pursue further the
history of research in the embryology of invertebrate animals, as may well be
seen from the following enumeration in an alphabetical order of the names of
some of the more prominent original observers, to whom has been mainly due
the great progress in this part of our science, viz., Agassiz, Alliman, Balbiani,
Edward van Beneden, P J. van Beneden, Victor Carus, Claparéde, Cohn,
Dalyell, Darwin, Dujardin, Ecker, Eschricht, Gegenbaur, Haeckel, Huxley,
Kölliker, Kowalewsky, Krohn, Lacaze Duthiers, Lereboullet, Leuckart, Leydig,
Lovén, Lubbock, Metschnikoff; Milne-Edwards, H. Müller, Johannes Müller,
Nordmann, Provost, Quatrefages, Salensky, Sars, Max Scbultze, Semper,
Steenstrup, Stein, C. Vogt, R Wagner, Strethill Wright. But this list includes
only a small part of the observers whose contributions to the knowledge of this
wide field of research would require to be noticed in any account of its
literature. The most general results which are deducible from numerous
observations which are now being accumulated in this department of
embryology may be briefly stated as follows.

In the Protozoa there is no true sexual generation, although in some the
phenomena of conjugation form an approach to that mode of reproduction, The
greater number usually multiply either by fission or by gemmation; but in some,
and probably in all, reproduction also appears to take place from extremely
minute particles separated from the parent animals, which can scarcely be
called ova, but which, for want of a better term, we may designate germinal
particles.

In all animals above the Protozoa, including the sponges, male and female
reproductive elements are to be distinguished, that of the female taking the form
of an ovum, in which the germinal part has the protoplasmic structure of a true
organized cell. Fecundation of the ovum takes place, as in all vertebrates, by the
direct access of the substance of the male element to the germinal part of the
ovum.

The first steps in the development of a fecundated ovum are in all instances
among the invertebrates, just as in the vertebrates, those of cellular
multiplication by fission or cleavage of the protoplasmic germ of the ovum,
which results in the formation of a more or less laminar blastoderm.

This blastoderm presents at first two layers of cells, ectoderm and endoderm, in
all animals above the Protozoa, and in the lowest of the Coelenterata only two ;
but in all the higher animals there appears an additional intermediate layer or
layers, constituting the mesoderm. From these layers the rudiments of the
several systems and organs of the body are developed by processes of cellular
multiplication and differentiation according to certain histological and
morphological laws essentially analogous to those which have been in part
previously referred to in this article, and which will be more fully described in
that on GENENATION.

Having now traced the principal steps by which, upon the basis of extended
morphological and histological observations during a century, extending from
Wolff to Darwin, the science of embryology has been securely founded, enough
has been adduced to show the important place which this science must occupy in
relation to other departments of biology. It will be seen that histology owes to
embryological observations the greatest amount of its recent extraordinary
progress. It is also apparent that many of the most important facts in
physiology, especially as related to growth and nutrition, can olily be
understood from a full and minute acquaintance with the various changes of
differentiation observed in the development of organic structure. It is equally
obvious that the nature of certain kinds of congenital malformation receive their
rational explanation in the knowledge of the natural organogenetic process of
development, from which they are no more than deviations in different modes
and degrees. Nor can it be doubted that the arrangement of animals under an
approved zoological system, in which the various affinities and gradations of
their organization are fully recognized, can only be undertaken upon the basis of
a complete knowledge of the metamorphoses of the young of animals and the
relation of the embryonic to the adult forms of the species. Lastly, the general
views which we may attempt to form of the process by which in the long lapse of
time since the creation the various kinds of animals, including man, may be
Supposed to have originated must be founded on the correlation of the
ascertained facts of embryology, as observed in every animal species, with the
fuller knowledge of the different forms and gradations of all existing animals,
and with the more complete observation of the different forms of organization,
the evidence of whose existence at successive periods of the earth's history is to
be found in their fossil remains which arc inclosed in the various strata
composing its superficial crust. (A. T.)